Plasmoid contamination in a Dense Plasma Focus

So I've been researching Dense Plasma Focus devices for a while now and a question just occured to me. Since the fill gass such as deuterium is being ionized and then compressed and fused in the Plasmoid, wouldn't some of the cathode material also be ionized and the trapped in the Plasmoid polluting it? If this is the case what equations would you use to calculate the number of cathod material atoms trapped in the Plasmoid in moles?